1. Field of the Invention
The present invention relates to a method for identification and management of errors and defects in assembly and welding lines for automotive vehicle bodies and body parts or the like. In particular the management concerns diagnosis and if necessary therapy of defects. The present invention also relates to a plant in accordance with said method.
2. State of the Prior Art
In the prior art, production lines for bodies and body parts made up of a plurality of automated precision assembly stations comprising a structure bearing a plurality of blocking inserts for mutual positioning of the parts to be assembled are well known. Assembly devices, for example articulated robot welding arms, fasten together permanently the parts positioned by the inserts and the finished product is then extracted from the station to pass to the following stations. Assembly can be accomplished by welding, gluing, riveting, seaming et cetera depending on specific requirements.
One of the more important problems met with on such lines is to ensure dimensional correctness of the product realized. Indeed, various factors contribute to making the object produced unlike the desired object. Degrading factors can be for example peculiar to the assembly technique used or due to geometrical changes occurring after the initial setting of one or more stations. For example, with assembly by welding, variations or drifting of the welding parameters such as those due to the consumption of the electrode, variation of the electrical current or welding time, change in position or sequence of performance of the welding points et cetera can occur. Similar factors can also be traced for the other assembly methods.
Geometrical variations can also be caused by maintenance work and/or adjustment of the stations, wear of movement parts or even variation of physical parameters of the parts being assembled (changes of composition, thickness, shape et cetera of the parts to be assembled). Typical is change of the thickness of parts pressed from sheet metal with change of the production lot.
To seek to reduce the number of defective products, sampling is usually done in the prior art by taking at intervals an article at the end of the line and inspecting it in special measuring stations to find the deviations from the “ideal” shape. If defects beyond the tolerable limits are found the line or part thereof is stopped and it is sought to trace back to the station or stations which produced the defect to then trace the cause of the defect within the station or stations thus identified. Lastly, the necessary corrective action is taken.
With such a manner of proceeding however, a certain number of defective articles are inevitably produced before the defect is found. Among other things, this involves waste of even complex parts already having passed through various perfectly successful processes and therefore perfectly acceptable up to the time of their assembly in the defective station. In addition, seeking the cause of the defect and its elimination require much time with resulting high costs of plant shutdown.
The general purpose of the present invention is to remedy the above mentioned shortcomings by making available a method and plant allowing efficient identification of errors, going back rapidly to the specific causes and, if necessary, information useful for their rapid and practical resolution.